The present invention relates to a method of gradual stopping control of an internal combustion engine, the piston in at least one cylinder of the engine being brought into a specific position which corresponds to an angular position of the crankshaft clearly located after the top dead center.
In internal combustion engines having internal direct start, in which the engine itself is used as a start motor, the piston in at least one cylinder must be in a position that is clearly after the top dead center. If fuel is subsequently injected into the cylinder and ignited, the resulting combustion torque is sufficient to start the engine. For such a direct start internal combustion engine, German Published Patent Application No. 197 41 294 proposes that in order to start the engine the crankshaft be brought into a predefined start position using an electric motor, so that the fuel injected into a start cylinder is ignited when the crankshaft start position is attained. Furthermore, this German Published Patent Application No. 197 41 294 also mentions that the piston position required for direct start can be set in at least one cylinder in a controlled manner as early as during the gradual stopping of the crankshaft. The above-named document does not describe the arrangement or the method whereby this specific stopping position can be achieved.
An object of the present invention is to provide a method of gradual stopping control of an internal combustion engine of the aforementioned type where the piston in at least one cylinder can be brought into a specific position during a gradual stopping of the internal combustion engine which allows direct start of the engine.
This object is achieved by the fact that the gas exhaust valves of one or more cylinders of the internal combustion engine are closed for one or more time segments after the ignition has been turned off, the beginning and the end of each valve closing segment being controlled so that the crankshaft remains in the desired stopping position. According to the present invention, in an internal combustion engine equipped with variable valve control, this valve control can also be used for gradual stopping control of the engine without the need for an additional arrangement.
According to the present invention, in a first method step, after the ignition has been turned off, the rotational speed of the crankshaft is measured after a predefined number of crankshaft revolutions as it passes through the top dead center. In a second method step, the gas exchange valves of the at least one cylinder are closed at the subsequent bottom dead center for a first valve closing segment. In a third method step, the rotational speed of the crankshaft is measured again as it passes through a predefined angular position after the bottom dead center. In a fourth method step, the end of the first valve closing segment is determined as a function of the two measured values of the rotational speed of the crankshaft. In the last method step, in the event of a rotational speed of the crankshaft, measured at the top dead center, corresponding to a maximum value of the kinetic energy, the gas exchange valves of at least one additional cylinder are closed for a second valve closing segment, the times of closing and opening of these gas exchange valves being determined as a function of the two measured values of the crankshaft rotational speed.
It is advantageous to read the end of the first valve closing segment from a first characteristic map, the beginning of the second valve closing segment from a second characteristic map, and the end of the second valve closing segment from a third characteristic map as a function of the difference of the two measured values of the rotational speed and the rotational speed of the crankshaft measured after the bottom dead center.
In a preferred embodiment, the first valve closing segment is terminated at an angular position of the crankshaft of 180xc2x0 before the predefined stopping position if the rotational speed measured at the top dead center corresponds to a minimum value of the kinetic energy, and the first valve closing segment is terminated at an angular position of the crankshaft of 90xc2x0 before the predefined stopping position if the rotational speed measured at the top dead center corresponds to a maximum value of the kinetic energy.
The second valve closing segment is advantageously begun in an angular position of the crankshaft of 90xc2x0 before the predefined stopping position and terminated in an angular position in the proximity of the stopping position if the rotational speed of the crankshaft measured at the top dead center corresponds to a maximum value of the kinetic energy.
It is advantageous to correct the beginning and ending points of the valve closing segments output by the characteristic maps using correction values taken from characteristic curves as a function of the engine temperature.